Converting Elemental Sulfur To Functional Polythioamides By Multicomponent Polymerization

The production of industrial sulfur is huge,but the flammable nature and oxidation property of sulfur make it unsuitable for long-term storage.The conversion and utilization of sulfur has hence become an urgent problem.At present,the commonly used melting diffusion method and inverse vaulcanization method generally require high temperature,and produce sulfur-containing materials with poor solubility and irregular structure,which has limited their development.Multicomponent polymerizations(MCPs),with the advantages of simple operation,efficient and mild reaction,and diverse product structures,have gradually developed into an efficient method for converting elemental sulfur to sulfur-containing functional polymers.Among the reported sulfur-containing polymers,polythioamides with a large number of hydrogen bonds,sulfur,and nitrogen atoms are a group of sulfur-containing materials with unique metal-coordination property and optical properties.This thesis is devoted to develop new multicomponent polymerizations for directly converting elemental sulfur to polythioamides,and further investigating the functionalities and applications of these polymer products.First of all,in view of the current problem that polythioamides can only be synthesized at high temperatures,we have developed a room temperature,catalyst-free multicomponent polymerization to directly convert elemental sulfur to polythioamides.Through the design of pyridine group-activated alkyne monomer,the MCPs of sulfur,alkyne,and aliphatic amine can be proceed smoothly at room temperature,affording polymer product with 98%yield and a M_wof 35 400 g/mol.Through the comparison of phenyldiyne monomer-or pyridine-activated diyne monomer-based MCPs,it is proved that the activated diyne monomer can polymerize smoothly at lower temperature with more dilute concentration,affording polythioamide with higher yield(98%)and higher M_ws(up to 95 100 g/mol).Owing to the unique coordination properties of thioamide and pyridyl groups to heavy metal ions,we utilized the synthesized polythioamides to adsorb Hg²⁺from aqueous solution,and the removal efficiency can reach 98.59%,which is improved compared with the previous report.We also find that the thioamide compounds and polymers in this work show photo-induced emission enhancement upon UV irradiation.Secondly,the reported sulfur-based MCPs are generally applicable to aliphatic amine monomers,which has limited the produced polymer structures.In order to make the MCP applicable for less nucleophilic aromatic amines for the construction of polythioamides with more rigid aromatic strucutres,we have developed a base-catalyzed MCP of aromatic amines,elemental sulfur and aromatic aldehydes.Through a series of optimization of conditions,8kinds of different polythioamides with thioamide groups directly linked to aromatic rings were obtained in high yields of up to 98%,and high M_w of up to 55 800 g/mol.The polythioamides enjoy good thermal stability with the highest thermal decomposition temperature to be 427 ^oC at 5%weight loss,and the carbon residue rate at 800 ^oC to be as high as 70%.Considering the strong binding ability of sulfur atom to gold ion,the polythioamides were utilized for the enrichment of gold ion from aqueous solution,and the enrichment efficiency is>99.99%,the enrichment capacity is 605 mg?Au³⁺/g.In summary,in view of the two current problems in the preparation of polythioamides from sulfur,we developed the MCP to synthesize polythioamides at room temperature through pyridyl-activated alkyne monomer design,and developed another MCP with base as catalyst to promote aromatic amines to participate in the MCP of sulfur.As a result,a variety of polythioamides with well-defined structures,high yields,and high M_ws were obtained,which further enriched the MCP of elemental sulfur and the polythioamide structures,providing an efficient,economic,and convenient strategy for the synthesis of sulfur-containing functional polymers.